Automatic control and antibacklash system

ABSTRACT

This invention relates to a system for controlling the rate of fluid flow within close tolerances while providing correction for backlash and includes mechanical means for controlling the rate of fluid flow, means for indicating the rate of fluid flow relative to prescribed limits, means for increasing the rate of fluid flow when the rate drops below the lower limit, and means for decreasing the rate of fluid flow when the rate goes above the upper limit. An antibacklash network is provided for removing slack or backlash in the mechanical control means whenever it, in making a correction, is made to operate in a reverse direction. The system further includes means for signalling malfunctions in the fluid system and for measuring the quantity of fluid flowing through the system.

United States Patent 11 1 Volk, Jr.

Jan. 2, 1973 [54] AUTOMATIC CONTROL AND ANTIBACKLASH SYSTEM [75]inventor: Joseph A. Volk, Jr., Florissant, Mo. I

63033 [73] Assignee: Beta Corporation of St. Louis, Mo.

Primary E xaminer llenry T. Klinksiek Attorney-Rogers, Ezell, Eilers &Robbins [57] ABSTRACT This invention relates to a system for controllingthe rate of fluid flow within close tolerances while provid- [22] Filed?Y Sept. 24, 1971 ing correction for backlash and includes mechanical[21] APPL No: 3 429 means for controlling the rate of fluid flow, meansfor indicating the rate of fluid flow relative to prescribed v imits,means for increasing the rate of fluid flow when [52] US. Cl ..137/2,137/4875 the rate dm 5 below the lower limit and means for 51 1 Cl F16k31 12 p liltdecreasing the rate of fluid flow when the rate g Fleld ofSearch bo he ppe n a ibac ash ne wo is PK vided for removing slack orbacklash in the mechani- [56] References C'ted cal control meanswhenever it, in making a correction, UNITED STATES PATENT is made tooperate in a reverse direction.- The system 3 357 428 2/1967 C I 137/4875 X further includes means for signalling malfunctions in I SO 3,369,56l2/1968 Zi mmef rman etaL. ....l37/487.5X flu'd.system for measur'ng thequam'ty of 3,454,037 7/1969 Grace et al ..137 4s7.5 flwmg thmugh system-19 Claims, 1 Drawing Figure 03 F 39 3f m 9 1 i'g ALARM i 4 20 J8 if-f f/y/ ALIKM SWITCH 0 DEV'CE TACH I0 20/ DECADE .1../ Ac POWER GENERATOR-"/5 ya 476 I92 COUNTER '03 SOURCE 201' 1 J /9 1 /90 a #6 //y w my A23fl DRIVE ANGLE 2/2 v 7 one SHOT A MULTIVIBRATOR BACKLASH' R A ONE SHOTBACKLASH Ac MULTIVIBRATOR STROBE FLIP-mar SWITCH by 7 9 I 1 /7/ /6/TRIGGER I /0 87 2:22;; 8 5? 0g A AC 410 423 6/ g) I C 49 SWITCH 97 6 ya5 93 I I I I 1.- 93/ 4 4 7/ 3; M6 0 r t SWITCH 83 a; a2

AUTOMATIC CONTROL AND ANTIBACKLASH SYSTEM SUMMARY OF THE INVENTION Oneof the problems with automatic control systems (for example those usedin controlling the rate 'of flow of a particular liquid) has been thedifficulty of providing control within close tolerances due to backlashor slack in the mechanical portions of the system. Backlash is inherentin any system where mechanical equipment such as motors, gear trains,and valves are used for providing the control. If the correction is madequickly enough to remove the backlash, the system usually overcorrectsfor normal control. On the other hand, if the corrections are made invery small intervals, it takes forever to remove the backlash and bythat time the flow rate may have changed appreciably. With thisinvention the backlash can be quickly removed while controlling the flowrate within very close tolerances.

The system generally includes a flow meter which measures the rate offlow of fluid through a fluid line. A valve in the fluid line controlsthe flow rate, which valve is driven by a gear train and motor. A meteris provided for indicating the flow rate in accordance with informationfrom the flow meter, and for setting the limits within which the rate isto be controlled.

A logic network initiates the generation of pulses of fixed widths froma drive angle multivibrator whenever the flow rate drops below the lowerlimit or above the upper limit, and gates these pulses to an appropriatetriac switch to close the switch for the duration of each pulse. Whenone of the triac switches is closed, AC power is applied across anappropriate motor winding within the motor causing it to turn in adirection to either open or close the valve in the fluid line. Thedirection the motor is made to rotate, of course, depends on whether thecorrection requires opening or closing the valve. This selection is madein accordance with the logic network.

Whenever the flow rate changes such that the meter indicator movesacross both the lower and upper limits, in either direction, themechanical components must be made to reverse direction to make thecorrection. In other words, the motor, gear train, and valve will bemade to rotate in a direction opposite to that in which it justpreviously rotated when making its last correction. When this conditionoccurs, there is a considerable amount of backlash in the mechanicalcomponents that must be removed before any noticeable correction is madein the rate of fluid flow. This condition is detected by the logicnetwork which generates signals causing a flip-flop to change state,thereby producing a strobe which initiates the generation of a backlashpulse from a backlash multivibrator. The width of this backlash pulse isadjusted in accordance with the amount of backlash in the system, but isusually of considerably longer duration than the pulses from the driveangle multivibrator used to make the flow rate corrections. This pulseis fed through the logic network and used to energize the motor for asufficient time to remove the backlash. After the backlash is removed,which occurs very quickly, the narrower width pulses from the driveangle multivibrator make the fine corrections in the flow rate, therebymaintaining very close 0 device.

tolerances while at the same time removing the backlash from the system.

DESCRIPTION or THE DRAWING The drawing is a schematic diagram of theautomatic control and antibacklash system of this invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT In the drawing there isshown a fluid flow control system 10 including a flow meter 12 connectedin a fluid feed line 14 for measuring the flow rate of the liquidthrough the line. The flow meter 12 includes an output shaft 16 whichdrives a tach generator 18, and

also a cam 20, the purpose for which will be hereinafter explained.

Also in the feed line 14 is a valve 24 which is preferably a ball typevalve, although other types such as shutter and gate valves couldbeused. The valve 24 is operated through a gear train 26 by a motor 28.Hence operation of the motor in one direction opens the valve, whileoperation of the motor in the other direction closes the valve. It isthe opening and closing of the valve 24 by operation of the motor 28that is controlled by this system to in turn control the rate of liquidflow through the feed line 14.

The tach generator 18 has an output conductor 34 connected through aconductor 35 to one input of a dual set point ammeter 36, and an outputconductor 38 connected through a potentiometer 39, a conductor 40 and aconductor 41 to another input of the ammeter 36. A capacitor 44 andresistor 45 are connected in parallel between the inputs of the meter36.

The meter 36 has a lower limit set pointer 48, an

upper limit set pointer 49 and an indicating needle 50.

It is of a standard type, commonly known in the-art, which indicates byappropriate signals at its outputs whether the indicating needle 50 isbelow, between, or above the pointers 48 and 49. The potentiometer 39and the resistor 45 are for the purposes of calibrating the meter 36.The capacitor 44 acts primarily as a filter.

When the indicating. needle 50 of the meter 36 moves upscale to aposition adjacent the upper limit pointer 49, a signal is fed through anoutput conductor 55, a pre-amp network 56, where the signal'isamplified, and a conductor 57 to the input of a Schmidt trigger 58. Whenthe indicating pointer 50 of the meter 36 moves downscale to a positionadjacent the lower limit pointer 48, a signal is fed through a conductor60, a pre-amp network 61 of the same type as the pre-amp network 56, anda conductor 62 to the input of another Schmidt trigger 63. Although thesignal on either the output conductor or from the meter 36 appears veryquickly, it nevertheless has a finite slope. The Schmidt triggers 58 and63 sense when the output signals from the pre-amps 56 and 61,respectively, reach a certain level and immediately produce at theiroutput a one level signal. The outputs of the Schmidt triggers 58 and 63go from a zero level to a one level in a matter of only a fewnanoseconds, so as to effectively sharpen the signal at the outputs ofthe pre-amps 56 and 61 for use in the network logic.

The output of the Schmidt trigger 58 is connected through a conductor 65to one input of an AND gate 67. The AND gate 67 has another inputconnected by a conductor 69 and a conductor 71 to the normally openterminal 72 of a double-pole, double-throw switch 73 having wiper arms74 and 75 connected to ground. The output from the Schmidt trigger 63 isconnected through a conductor 80 to one input of an AND gate 82 havinganother input connected by a conductor 83 and the conductor 71 to thenormally open terminal 72 of the switch 73. The output from the AND gate67 is connected through a conductor 85, a conductor 86, an inverter 87,and a conductor 88 to one input of an AND gate 90. The output from theAND gate 82 is connected through a conductor 92, a conductor 93, aninverter 94, and a conductor 95 to the other input of the AND gate 90.

The output from the AND gate 67 is also connected through the conductor85, a conductor 96, and a conductor 97 to one input of an AND gate 100.The output of the AND gate 82 is also fed through the conductor 92, aconductor 101, and a conductor 102 to one input of an AND gate 104.

The output from the AND gate 90 is connected through a conductor 106, aconductor 107, an inverter 108, and a conductor 109 to the input of anoscillator 110. As long as the input of the oscillator 1l0'is at a onelevel, the oscillator generates a series of sharp pulses, the frequencyof which is adjustable with a poten-' tiometer control 112. The exactfrequency used depends on such factors as the viscosity of the fluid andthe pressure drop across the fluid inlet and outlet. A frequency rangeof between two pulses per second and one pulse every two seconds is anexample ofa normal range. When the signal at its input is at a zerolevel, the oscillator 110 is inhibited. As will be seen, this occurswhenever the indicating needle 50 is within the accepted range betweenthe pointers 48 and 49. Whenever the needle 50 moves below the pointer48 or above the pointer 49, the oscillator 110 is enabled.

The output pulses from the oscillator 1l0are fed through a conductor 114to a drive angle, one shot multi-vibrator 116 which produces a pulse,the width of which is adjustable by a potentiometer control 118, foreach pulse received at its input from the oscillator 110. The pulsesfrom the multivibrator 116 are fed through a conductor 120, a conductor121, an OR gate 122, a conductor 123, and a conductor 124 to the otherinput of the AND gate 100; and through a conductor 125 to the otherinput of the AND gate 104.

As will be explained, whenever the flow rate becomes excessive, that is,whenever the indicator 50 moves past the pointer 49, the AND gate 100 isenabled, and whenever the flow rate becomes too low, that is, wheneverthe indicator 50 moves below the pointer 48, the AND gate 104 isenabled. When the AND gate 100 is enabled, a signal is fed from itsoutput through a conductor 130 to the gate of a triac AC switch 131. Thetriac switch 131 has an output connected by a conductor 132 and aconductor 133 to a winding of the motor 28 which, when energized with ACpower,

causes the motor 28 to turn in a direction to close the valve 24. In asimilar manner, when the AND gate 104 is enabled, a signal is fed fromits output through a conductor 135 to the gate input of a triac ACswitch 137. The switch 137 has an output connected by a conductor 139and a conductor 140 to another winding of the motor 28 which, whenenergized with AC power, causes the motor to turn in a direction to openthe valve 24. Both windings of the motor 28 are connected through aconductor 141 and a conductor 142 to a source of AC power. The triacswitches 131 and 137 are such that a signal at their gate inputs connecttheir outputs to ground. Hence, when the switch 131 is enabled, AC powerfrom the power source energizes one motor winding, and when the switch137 is enabled, AC power from the power source enables the other motorwinding.

Another normally open terminal of the manual switch 73 is connected by aconductor 151 to the wiper arm 152 of a manual switch 153. One normallyopen contact 154 of the switch 153 is connected by a conductor 155 tothe conductor 140 leading to one winding of the motor 28. Anothernormally open contact 156 of the switch 153 is connected by a conductor157 to the conductor 133 leadingto the other winding of the motor 28. Aswill be explained, by placing the switch 73 in its normally openposition, the automatic circuit is disabled, and by manually operatingthe switch 153 to engage thecontact 154 or 156, one side of a winding ofthe motor 28 is grounded to cause the valve 24 to open or close asdesired. This would be useful, for example, if there is a breakdown inthe automatic network.

An important feature of this invention is the antibacklash network. Thecombination of the motor 28, gear train 26, and valve 24 has inherentlyassociated with it a certain amount of backlash, or slack. As long asthe motor is running in one direction, this backlash is no problem, noris it a problem where the motor was first running in one direction, thenstopped, and then again run in that same direction. The problem onlyarises where the motor is first made to run in one direction, and thenin the opposite direction. The only time this is required is when theindicating needle 50 moves completely across both set pointers 48 and49, for this is the only time that the valve 24 must be made to eitherclose from a just-prior opening operation, or open from a just-priorclosing operation. For example, if the needle 50 is below the pointer48, the network of this'system will open the valve to increase the fluidflow, and to 'move the needle 50 upscale. If the needle 50 again movesbelow the pointer 48, the system will open the valve 24 still more, andthere will be no slack to take up. But if the increase in fluid floweventually causes the needle 50 to move above the pointer 49, the systemwill close the valve requiring the motor and gear train to reversedirections as well so that there will be a certain amount of slack orbacklash that must be taken up before flow rate control can begin. Thesame, of course, is true if the needle 50 begins above thepointer 49.Here the system will close the valve 24 causing fluid flow to decreaseand the needle 50 to movebelow the pointer 49. If the fluid flow laterincreases the needle 50 will again move above the pointer 49, the systemwill tend to close the valve 24 all the more, and there will be no slackto take up. But if instead the needle 50 moves further downscale to aposition below the pointer 48, the system will open the valve 24reversing the directions of the gear train and motor as well so thatthere will be slack and backlash to take up before flow rate control canbegin.

Without the antibacklash feature of this invention it would be verydifficult, if not virtually impossible, to achieve a fine flow ratecontrol (within approximately one-half percent), because with such finecontrol it would take too long to remove the backlash whenever theneedle 50 moves across both pointers. By the time the system made thecorrection, the flow rate might be greatly changed. However, theantibacklash network of this invention provides such control.

The output of the AND gate 67 is also connected through the conductors85 and 96,, and a conductor 161 to one input ofa backlash flip-flop 162.The output of the AND gate 82 is fed through the conductors 92 and 101,and a conductor 166 to the other input of the flip-flop 162. The onlytime the outputs of the flip-flop 162 change state is when the signalsat its inputs change state, and this is only when the needle 50 movescompletely across the pointers 48 and 49. The flip-flop 162 has anoutput connected by a conductor 167 to the input of strobe 169, and anoutput connected by a conductor 171 to the input ofa strobe 173. Whenthe input to the strobe 169 or 173 goes from a one level to a Zero levelthe strobe produces at its output a strobe pulse, which, in the case ofthe strobe 169 is fed through a conductor 175 to one input of an OR gate177, and in the case of the strobe 173 is fed through a conductor 179 toanother input of the OR gate 177. Hence, one of the strobes 169 or 173generates a strobe pulse whenever the needle 50 moves from below thepointer 48 to above the pointer 49, and the other generates a strobepulse whenever the needle 50 moves from above the pointer 49 to belowthe pointer 48. These strobe pulses are fed through the OR gate 177 tothe input of a backlash one shot multivibrator 181 which produces at itsoutput, for each such strobe pulse, a pulse having a width adjustable bya control potentiometer 183. The pulse from the output of themultivibrator 181 is fed through a conductor 185, the OR gate 122, andthe conductor 123 to the AND gates 100 and 104, just as the pulses fromthe output of the multivibrator 116. The width of the pulse at theoutput of the multivibrator 181 is adjusted to suit the amount ofbacklash in the system and will normally be several times (perhaps ortimes) greater than the widths of the pulses from the multivibrator 116used to make the flow rate corrections.

The network of this invention also includes an alarm system forsignalling a possible malfunction in the flow system. This might occur,for example, when the valve 24 is malfunctioning or a filter screen inthe flow pipe has become clogged. When such things occur, the system, ofcourse, is unable to make the required correction. The alarm networksignals such a condition.

The output pulses from the multivibrator 116 are fed through theconductor 120 and a conductor 190 to one input of an AND gate 192, theoutput of which is connected through a conductor 194 to an alarm decadecounter 196. The counter 196 counts the pulses from the multivibrator116 until it reaches some predetermined count, which may be set asdesired. For example, if it is determined that any correction should bemade with no more than eight pulses from the multivibrator 116, then thecounter 196 would be set to count up to eight. When the count reacheseight, a signal appears at the output of the counter 196 which is fedthrough a conductor 197 and a conductor 198 to the gate of a triac ACswitch 199, as well as through a conductor 200 and an inverter 201 tothe other input of the AND gate 192. The switch 199 has an outputconnected by a conductor 202 to the input of an alarm device 203, theoutput of which is connected by a conductor 204 to a source of AC power.When the counter 196 reaches the set count, the signal at its outputcloses the switch 199, grounding the input side of the alarm device 202,thereby turning it on. The alarm device 203 may be a siren, a bell, abuzzer, a light signal, or some other suitable electrical signallingdevice. The signal from the inverter 201 inhibits the AND gate 192 tohold the counter 196 at an eight count and the alarm 203 on.

The output of the AND gate is connected through the conductor 106 and aconductor 205 to a clear input of the counter 196. When the output ofthe AND gate 90 is at a one level, which, as will be seen, occurs whenthe indicating needle 50 is between the pointers 48 and 49, the alarmdecade counter 196 is cleared, the switch 199 opened, and the alarmdevice 203 is deenergized.

The system also includes a network for measuring the quantity of fluidthat flows past the meter 12. The cam 20 is geared to make onerevolution each time a predetermined amount of fluid, for example onepound, flows past the meter 12. As the cam 20'makes a revolution itcloses a limit switch 210 which connects +5 v. on a conductor 211through the switch 210 and a conductor 212 to the gate of a triac ACswitch 214. The output of the switch 214 is connected by a conductor 216to the input of the counter totalizer 218. The other side of the counter218 is connected by a conductor 220 and the conductor 142 to the sourceof AC power. Each time the triac switch 214 is closed by the closing ofthe limit switch 210 as operated by the cam 20, AC power is placedacross the counter totalizer 218 causing it to register another count.At any given time the totalizer 218 visually indicates the total numberof pounds that have flowed past the meter 12 in a given period.

OPERATION To operate the system in the automatic mode the manual switch73 is placed in the normally closed position as shown in the drawing,the limit pointers 48 and 49 are set to control the rate of fluid flowwithin the desired limits, the widths of output pulses from themultivibrator 116 are adjusted to provide the normal flow correctiondesired, and the width of the outputpulse from the backlashmultivibrator 181 is set to provide an initial backlash correctioncommensurate with the amount of slack or backlash in the system. Theammeter 36 is calibrated by adjusting the potentiometer 39.

As fluid flows through the conduit 14 and passes the meter 12, the rateof this flow is indicated by the indicating needle 50 of the meter 36.As long as the needle 50 is between the pointers 48 and 49 there are nosignals to the inputs of the preamps 56 and 61 or at the outputs of theSchmidt triggers 58 and 63, and hence the AND gates 67 and 82 aredisabled. With these gates disabled, their outputs are at a zero levelcausing there to be no change in state of the backlash flip-flop 162 andno correction for backlash. The gates 100 and 104 are also disabled sothat the AC switches 131 and 137 remain open and the motor 28inoperable. Also, with the outputs of the AND gates 67 and 82 at zerolevels, the inputs of the AND gate 90 are at one levels, these signalshaving gone through the invertors 87 and 94, producing a one levelsignal at the output of the AND gate 90 which is fed through theconductor 106 and the conductor 107 to the input of the invertor 108.The output of the invertor 108 is therefore at a zero level whichinhibits the oscillator 110. With the oscillator 110 inhibited there areno pulses generated at the output of the multivibrator 116 to makecorrections. Hence, as long as the indicating needle 50 is between thepointers 48 and 49 all is going well and the correction control networkremains inoperative.

If the needle 50 moves above the pointer 49 a signal is fed through theconductor 55 to the preamp 56 where it is amplified, and then to theSchmidt trigger 58. The output of the Schmidt tripper 58 is a one levelsignal which enables the AND gate 67 producing a one level signal at itsoutput which is inverted by the inverter 87 to a zero level at itsoutput which is inverted to a one level signal by the invertor 108 toenable the oscillator 110. For each pulse from the oscillator 110 themultivibrator 116 produces a pulse of the selected width which is fedthrough the OR gate 122 to an input of each of the AND gates 100 and104. The one level output from the AND gate 67 is also fed through theconductor 97 to the other input of the AND gate 100, enabling the ANDgate 100 and producing a one level signal at its output for the durationof each pulse from the multivibrator 116. These one level signals closethe triac switch 131 causing the motor 28 to operate in a directiontending to close the valve 24. Hence for each pulse from themultivibrator 116, the motor 28 turns a prescribed length of time toclose the valve 24 a predetermined amount.

As the valve 24 closes, the rate of fluid flow is reduced as indicatedby the flow meter 12 and indicating needle 50. The needle 50 willtherefore begin to move downscale. As soon as it moves to a positionjust below the pointer 49, the signal on the output conductor 55 fromthe meter 36 goes to zero, and the output of the AND gate 67 goes to azero level. This disables the AND gate 100 so that the triac switch 131remains open and the motor 128 deenergizes. Also, the output of the ANDgate 90 goes to a one level inhibiting the oscillator 110 so that nocorrection pulses are produced at the output of the multivibrator 116.

As long as the fluid flow rate stays within the prescribed limits, theautomatic control network will make no further corrections. However,suppose that the rate of flow decreases to where the needle 50 movesbelow the pointer 48. When this occurs, a signal is produced at theoutput conductor 60 from the meter 36 which is fed through the preamp61, where it is amplified. The amplified signal is fed to the Schmidttrigger 63 producing a one level signal which is fed to the AND gate 82.With the AND gate 82 enabled, the one level signal is fed through theconductors 92, 101 and 166 to one input of the backlash flip-flop 162.

At this point it will be remembered that the needle 50 has traveled fromabove the pointer 49 to below the pointer 48. This meets the conditionof the needle moving completely across both pointers, which aspreviously explained, is the one condition where the motor 28, geartrain 26, and valve 24 change direction and there is backlash in thesystem. When the needle 50 was above the pointer 49, the input conductor161 to the flip-flop 162 was at a one level and the input conductor 166was at a zero level. Now that the indicating needle 50 is below'thepointer 48, the signal on the input conductor 161 is at a zero level andthe signal on the conductor 166 is at a one level. Since the inputsignals to the flip-flop 162 are now reversed, its output signals alsoreverse, causing a strobe pulse to be generated at the output of one ofthe strobes 169 and 173. This strobe pulse is fed through the OR gate177 to the backlash multivibrator 181, producing a pulse of the selectedwidth. This pulse, which is of considerably longer duration than a pulsefrom the output of the multivibrator 116, is fed through the OR gate 122to one input of each of the AND gates 100 and 104.

The one level output from the AND gate 82 is also fed through theconductor 102 to the other input of the AND gate 104 enabling the gateand producing a one level signal at its output that closes the triacswitch 137 for the duration of the backlash pulse. During this time, themotor operates in the direction opposite to that in which it justpreviously operated to remove the backlash from the gear train 26.

In the meantime, the one level output from the AND gate 82 is invertedby the invertor 94, the zero level output of which disables the AND gate90. With the AND gate disabled, its output drops to a zero levelproducing a one level signal at the output of the invertor 108 to enablethe oscillator 110. The oscillator 110 and the multivibrator 116 thenoperate inthe same manner as with the indicating needle 50 above thepointer 49 to produce correction pulses of fixed width which are fed tothe AND gates and 104. With the AND gate 104 enabled, each of thesepulses closes the triac switch 137 to cause the motor 28 to rotate in adirection tending to openthe valve 24. These correction pulses continueuntil the rate of fluid flow increases to where the needle 50 is abovethe pointer 48, at which time the signal on the output conductor 60 fromthe meter 36 will drop to zero and the pulses from the multivibrator 116 will cease.

It will be noted that while the multivibrator 116 is made to generatepulses until correction is made to within the prescribed limits, themultivibrator 181 produces only a single pulse of sufficient width toremove the backlash. The anti-backlash network will not again beactivated unless the needle 50 moves above the pointer 49. If thisshould occur, it would have again moved across both pointers 48 and 49,the output of the backlash flip-flop 162 would again change state, astrobe would be generated, and a backlash pulse would be fed through theAND gate 100 to cause the motor to drive in the opposite direction toremove slack in the gear train 26.

Whether the needle 50 is below the pointer 48 or above the pointer 49,the output pulses from the multivibrator 1 16 are fed through the ANDgate 192 to the alarm decade counter 196. When the count reaches aprescribed number, the triac switch 199 is closed and the alarm device203 activated, indicating trouble in the system and the system'sinability to make the correction. If the needle 50 should drop backbetween the limits 48 and 49, the output of the AND gate 90 goes to aone level to clear the decade counter 196 and deenergize the alarm 203.

The counter 196 can also be cleared by placing the manual switch 73 inthe normally open position. This forces one of the inputs of each of theAND gates 67 and 82 to ground, thereby disabling these gates andproducing a one level signal at the output of the AND gate 90.

Placing the switch 73 in the normally open position also places thesystem in the manual mode, for, regardless of the position of the needle50, the AND gates 67 and 82 remain disabled. This effectively disablesthe automatic control network. Then by moving the switch 153 in contactwith the terminal 154, the motor 28 is made to rotate in a directiontending to open the valve 24, and by moving the switch 153 in contactwith the terminal 156, the motor 28 is made to rotate in a directiontending to close the valve 24. Hence, by manually operating the switch153, the rate of flow can be controlled within the prescribed limits.

As previously explained, the cam 20, switch 210, triac switch 214 andcounter totalizer 218 are continuously operating to measure the quantityof fluid moving past the meter 12.

Therefore, a system has been described for providing control withinextremely close tolerances while providing correction for slack orbacklash in the system.

Various changes and modifications may be made within this invention, aswill be readily apparent to those skilled in the art. Such changes andmodifications are within the scope and teaching of this invention asdefined by the claims appended hereto.

What is claimed is:

l. A method for controlling a particular variable of an operation havingmechanical backlash, comprising the step of detecting changes in thevariable being controlled, indicating a measure of these changes inrelation to upper and lower limits within which the variable is to becontrolled, generating electrical correction signals whenever thevariable varies outside these limits, correcting the variable to withinthe limits in response to the electricalcorrection signals, generatingan electrical backlash signal whenever the variable varies across bothlimits,and correcting the operation for mechanical backlash in responseto the backlash signal.

2. An automatic control system for controlling the rate of fluid flowthrough a fluid line of a fluid system characterized as having backlash,the control system comprising means for measuring the flow rate of thefluid in relation to limits within which the flow rate is to becontrolled, a valve means in the fluid line for controlling the flowrate of the fluid, a motor connected to the valve means such thatoperation of the motor in one direction tends to open the valve means,and operation of the motor in the opposite direction tends to close thevalve means, means for generating electrical correction signals wheneverthe measuring means indicates a flow rate outside the limits, means foroperating the motor means in response to the signals in a direction tocause the flow rate to change to within the prescribed limits, means forgenerating an electrical backlash signal whenever the flow rate variesacross both limits, and means for operating the motor means in responseto the backlash signal in a direction to remove the backlash from thesystem.

3. The automatic control system of claim 2 including means forinhibiting the signal generating means whenever the flow rate is withinthe limits.

4. The system of claim 2 wherein the measuring means includes an ammeterhaving upper and lower limit sets, the ammeter including means togenerate a signal at one output whenever the meter indicates ameasurement below the lower set, and means for generating a signal atanother output whenever the meter indicates a measurement above theupper set.

5. The system of claim 4 wherein the measuring means further includes atach generator, a flow meter for detecting the rate of fluid flow, meansassociated with the flow meter for driving the tach generator at a rateproportional to the flow rate, the tach generator including means forgenerating electrical signals proportional to the rate at which it isdriven, and means for feeding the electrical signals from the tachgenerator to the ammeter for indicating the flow rate of the fluid.

6. The system of claim 2 wherein the motor means includes a motor havinga first winding which when energized causes the motor to operate in aclockwise direction, and a second winding which when energized causesthe motor to operate in a counterclockwise direction, and including agear train mechanically connected between the motor means and the valvemeans.

7. The system of claim 2 including means for measuring the quantity offluid through the fluid system.

8. The system of claim 2 including means for signalling a malfunction inthe fluid system.

9. The system of claim 8 wherein the signalling means includes means forcounting the number of correction signals, means for generating a signalwhen the count reaches a prescribed number, electrical signalling means,and means responsive to the last named signal -for activating theelectrical signalling means. v

10. The system of claim 2 including an oscillator means for generating acontinuous series of pulses when enabled, means for enabling theoscillator means whenever the-flow rate varies to outside the limits,and means for generating the correction signals in response to theoutput pulses from the oscillator means.

11. The system of claim 10, including means for adjusting the'frequencyof the output pulses from the oscillator means.

12. The system of claim 10 including means for inhibiting the oscillatormeans whenever the flow rate is within the prescribed limits.

13. The system of claim 10 wherein the correction signals are pulses ofselected widths.

14. The system of claim 2 including a flip-flop, means for changing thestate of the flip-flop output whenever the flow rate varies across bothlimits, means for generating a strobe whenever the output of theflip-flop changes state, and means for generating the backlash signal inresponse to the strobe.

15. The system of claim 14 including means for adjusting the duration ofthe backlash signal.

16. The system of claim 2 including first and second switching means,means for causing the motor to operate in a direction so as to close thevalve means whenever the first switching means is closed, means forcausing the motor to operate in a direction so as to open the valvemeans when the second switching means is closed, a gating network, meansassociated with the gating network for gating the correction signals toclose the first switching means whenever the flow rate increases abovethe upper limit, and. means associated with the gating network forgating the correction signals to close the second switching meanswhenever the flow rate decreases below the lower limit.

17. The system of claim 16 further including means associated with thegating network for gating the backlash signal to close the firstswitching means whenever the flow rate increases across both limits, andmeans associated with the gating network for gating the backlash signalto open the second switching means whenever the flow rate decreasesacross both limits.

18. The system of claim 2, including means for disabling the automaticcontrols system, a manual switch, and means responsive to operation ofthe manual switch for causing the motor to operate in a selecteddirection.

19. A method for controlling the rate of fluid flow through a fluid lineof a fluid system characterized as having backlash, comprising the stepof measuring the flow rate of the fluid in relation to limits withinwhich the flow rate is to be controlled, generating electricalcorrection pulses of selected widths whenever the flow rate varies tooutside the limits, operating a motor in response to the correctionpulses in a direction to cause the flow rate to change to within theprescribed limits, generating an electrical backlash signal whenever theflow ate varies across both limits, and operating the motor in responseto the backlash signal in a direction to remove the backlash from thesystem.

1. A method for controlling a particular variable of an operation havingmechanical backlash, comprising the step of detecting changes in thevariable being controlled, indicating a measure of these changes inrelation to upper and lower limits within which the variable is to becontrolled, generating electrical correction signals whenever thevariable varies outside these limits, correcting the variable to withinthe limits in response to the electrical correction signals, generatingan electrical backlash signal whenever the variable varies across bothlimits, and correcting the operation for mechanical backlash in responseto the backlash signal.
 2. An automatic control system for controllingthe rate of fluid flow through a fluid line of a fluid systemcharacterized as having backlash, the control system comprising meansfor measuring the flow rate of the fluid in relation to limits withinwhich the flow rate is to be controlled, a valve means in the fluid linefor controlling the flow rate of the fluid, a motor connected to thevalve means such that operation of the motor in one direction tends toopen the valve means, and operation of the motor in the oppositedirection tends to close the valve means, means for generatingelectrical correction signals whenever the measuring means indicates aflow rate outside the limits, means for operating the motor means inresponse to the signals in a direction to cause the flow rate to changeto within the prescribed limits, means for generating an electricalbacklash signal whenever the flow rate varies across both limits, andmeans for operating the motor means in response to the backlash signalIn a direction to remove the backlash from the system.
 3. The automaticcontrol system of claim 2 including means for inhibiting the signalgenerating means whenever the flow rate is within the limits.
 4. Thesystem of claim 2 wherein the measuring means includes an ammeter havingupper and lower limit sets, the ammeter including means to generate asignal at one output whenever the meter indicates a measurement belowthe lower set, and means for generating a signal at another outputwhenever the meter indicates a measurement above the upper set.
 5. Thesystem of claim 4 wherein the measuring means further includes a tachgenerator, a flow meter for detecting the rate of fluid flow, meansassociated with the flow meter for driving the tach generator at a rateproportional to the flow rate, the tach generator including means forgenerating electrical signals proportional to the rate at which it isdriven, and means for feeding the electrical signals from the tachgenerator to the ammeter for indicating the flow rate of the fluid. 6.The system of claim 2 wherein the motor means includes a motor having afirst winding which when energized causes the motor to operate in aclockwise direction, and a second winding which when energized causesthe motor to operate in a counterclockwise direction, and including agear train mechanically connected between the motor means and the valvemeans.
 7. The system of claim 2 including means for measuring thequantity of fluid through the fluid system.
 8. The system of claim 2including means for signalling a malfunction in the fluid system.
 9. Thesystem of claim 8 wherein the signalling means includes means forcounting the number of correction signals, means for generating a signalwhen the count reaches a prescribed number, electrical signalling means,and means responsive to the last named signal for activating theelectrical signalling means.
 10. The system of claim 2 including anoscillator means for generating a continuous series of pulses whenenabled, means for enabling the oscillator means whenever the flow ratevaries to outside the limits, and means for generating the correctionsignals in response to the output pulses from the oscillator means. 11.The system of claim 10, including means for adjusting the frequency ofthe output pulses from the oscillator means.
 12. The system of claim 10including means for inhibiting the oscillator means whenever the flowrate is within the prescribed limits.
 13. The system of claim 10 whereinthe correction signals are pulses of selected widths.
 14. The system ofclaim 2 including a flip-flop, means for changing the state of theflip-flop output whenever the flow rate varies across both limits, meansfor generating a strobe whenever the output of the flip-flop changesstate, and means for generating the backlash signal in response to thestrobe.
 15. The system of claim 14 including means for adjusting theduration of the backlash signal.
 16. The system of claim 2 includingfirst and second switching means, means for causing the motor to operatein a direction so as to close the valve means whenever the firstswitching means is closed, means for causing the motor to operate in adirection so as to open the valve means when the second switching meansis closed, a gating network, means associated with the gating networkfor gating the correction signals to close the first switching meanswhenever the flow rate increases above the upper limit, and meansassociated with the gating network for gating the correction signals toclose the second switching means whenever the flow rate decreases belowthe lower limit.
 17. The system of claim 16 further including meansassociated with the gating network for gating the backlash signal toclose the first switching means whenever the flow rate increases acrossboth limits, and means associated with the gating network for gating thebacklash signal to open the second switching means whenever the flowrate decreaseS across both limits.
 18. The system of claim 2, includingmeans for disabling the automatic controls system, a manual switch, andmeans responsive to operation of the manual switch for causing the motorto operate in a selected direction.
 19. A method for controlling therate of fluid flow through a fluid line of a fluid system characterizedas having backlash, comprising the step of measuring the flow rate ofthe fluid in relation to limits within which the flow rate is to becontrolled, generating electrical correction pulses of selected widthswhenever the flow rate varies to outside the limits, operating a motorin response to the correction pulses in a direction to cause the flowrate to change to within the prescribed limits, generating an electricalbacklash signal whenever the flow ate varies across both limits, andoperating the motor in response to the backlash signal in a direction toremove the backlash from the system.